1. Field of the Invention
The present invention relates to a crucible for a LUWPL, that is a Lucent waveguide Plasma Light source.
2. Description of the Related Art
In European Patent No EP1307899, granted in our name there is claimed a light source comprising a waveguide configured to be connected to an energy source and for receiving electromagnetic energy, and a bulb coupled to the waveguide and containing a gas-fill that emits light when receiving the electromagnetic energy from the waveguide, characterized in that:
(a) the waveguide comprises a body consisting essentially of a dielectric material having a dielectric constant greater than 2, a loss tangent less than 0.01, and a DC breakdown threshold greater than 200 kilovolts/inch, 1 inch being 2.54 cm,
(b) the wave guide is of a size and shape capable of supporting at least one electric field maximum within the wave guide body at at least one operating frequency within the range of 0.5 to 30 GHz,
(c) a cavity depends from a first side of the waveguide,
(d) the bulb is positioned in the cavity at a location where there is an electric field maximum during operation, the gas-fill forming a light emitting plasma when receiving microwave energy from the resonating waveguide body, and
(e) a microwave feed positioned within the waveguide body is adapted to receive microwave energy from the energy source and is in intimate contact with the waveguide body.
In our European Patent No 2,188,829 there is described and claimed a light source to be powered by microwave energy, the source having:                a body having a sealed void therein,        a microwave-enclosing Faraday cage surrounding the body,                    the body within the Faraday cage being a resonant waveguide,                        a fill in the void of material excitable by microwave energy to form a light emitting plasma therein, and        an antenna arranged within the body for transmitting plasma-inducing, microwave energy to the fill, the antenna having:        a connection extending outside the body for coupling to a source of microwave energy;wherein:        the body is a solid plasma crucible of material which is lucent for exit or light therefrom, and        the Faraday cage is at least partially light transmitting for light exit from the plasma crucible,the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the cage.        
We refer to this as our Light Emitting Resonator or LER patent. Its main claim as immediately above is based, as regards its prior art portion, on the disclosure of our EP1307899, first above.
In our European Patent Application No 08875663.0, published under No W02010055275, there is described and claimed a light source comprising:                a lucent waveguide of solid dielectric material having:                    an at least partially light transmitting Faraday cage surrounding the waveguide, the Faraday cage being adapted for light transmission radially.            a bulb cavity within the waveguide and the Faraday cage and            an antenna re-entrant within the waveguide and the Faraday cage and            a bulb having a microwave excitable fill, the bulb being received in the bulb cavity.                        
We refer to this as our Clam Shell application, in that the lucent wave guide forms a clam shell around the bulb.
As used in our LER patent, our Clam Shell application and this specification:                “microwave” is not intended to refer to a precise frequency range. We use “microwave” to mean the three order of magnitude range from around 300 Mfl/to around 300 GHz;        “lucent” means that the material, of which an item described as lucent is comprised, is transparent or translucent;        “plasma crucible” means a closed body enclosing a plasma, the latter being in the void [in the body] when the void's fill is excited by microwave energy from the antenna;        “Faraday cage” means an electrically conductive enclosure of electromagnetic radiation, which is at least substantially impermeable to electromagnetic waves at the operating, i.e. microwave, frequencies.        
The LER patent, the Clam Shell Application and certain LER improvement applications have in common that they are in respect of:
A microwave plasma light source having:
                a Faraday cage:                    delimiting a waveguide and            being at least partially lucent, and normally at least partially transparent for light emission from it and            normally having a non-lucent closure:                        a body of solid-dielectric, lucent material embodying the waveguide within the Faraday cage;        a closed void in the waveguide containing microwave excitable material; and        provision for introducing plasma exciting microwaves into the waveguide:the arrangement being such that on introduction of microwaves of a determined frequency a plasma is established in the void and light is emitted via the Faraday cage.        
In our patent application No. PCT/GB2011/001744 (our '744 Application), we defined an LUWPL as follows:
A microwave plasma light source having:
                a fabrication of solid-dielectric, lucent material, having;        a closed void containing electro-magnetic wave, normally microwave excitable material; and        a Faraday cage:        delimiting a wave guide,        being at least partially lucent, and normally at least partially transparent, for light emission from it,        normally having a non-lucent closure and        enclosing the fabrication;        provision for introducing plasma exciting electro-magnetic waves, normally microwaves, into the waveguide;the arrangement being such that on introduction of electro-magnetic waves, normally microwaves, of a determined frequency a plasma is established in the void and light is emitted via the Faraday cage.        
In the preferred embodiment of our LER patent, the void is formed directly in the lucent waveguide, which is generally a quartz body. This exposes the quart material to high temperatures by radiation from the plasma and conduction from the gases surrounding the plasma. It is because of this exposure that the term “solid plasma crucible” is used in the LER patent, a crucible being a container for high temperature material. This exposure can result in problems if the plasma causes micro-cracking of the material of the crucible, which then propagate through it.
In our Clam Shell application, this problem is not so apparent in that a quartz bulb having the void and excitable material is provided distinct from and inserted into the lucent wave guide. The waveguide may be formed of two halves captivating the bulb between them or a single body having a bore in which the bulb is received.